In recent years, digital electronic devices have been improved in precision and sensitivity with greater compactness, attaching greater importance to protection against electromagnetic noises.
Furnishing a cable core with a shield layer around it is a common way of protecting a cable from electromagnetic noises. Shield layers which have been used heretofore include braided threads of tin-plated annealed copper, a copper tape wound around the core, an aluminum pipe, a polyester tape with evaporated aluminum or copper thereon wound around or aligned along the core, coating of conductive composition containing carbon or metal particles.
A double-layered shield consisting of a laminated metal-plastic tape, such as a laminated aluminum-polyester tape, and a metal shield formed of braided or wound metal wires has been used frequently, not only for shielding but for preventing moisture from coming into the core to improve the line reliability.
For instance, a cable core consisting of stranded wires each having a conductor covered with an insulation layer is surrounded with a shield consisting of a laminated aluminum-polyester tape and a braided metal wire, further covered with a protective sheath.
Braiding of metal strands is carried out only at a limited speed because the operation of braiding a plurality of metal wires is rather complicated. As the process of braiding metal wires follows the processes of core stranding and tape winding which can be carried out at higher speeds, storage of the core in reservoir bobbins prior to braiding is required, thus the overall efficiency of manufacturing process being lowered.
Terminal handling for connection, branching etc. of the cable lines requires removal of braided wire shield in a certain length from an end of the cable. The braided wires which form a cylindrical layer in close contact with the core have to be removed by a special scissor-like tool by a laborious operation.
Flexibility of a cable is lowered by the braided shield attached thereto, more remarkably with the increasing density of braiding, because the wire strands are braided in a cylindrical shape in close contact with the cable core.